To meet increasingly stringent diesel exhaust emissions requirements, original equipment manufacturers (OEMs) have introduced common rail fuel injection systems that develop pressures of up to 2000 bar (29,000 psi). In addition, fuel delivery schemes have become more complicated, often involving multiple injections per cycle. Fuel injectors using higher pressures and allowing for precise metering of fuel require very tight tolerances within the injector. For example, high pressure fuel injectors may have an average injector hole diameter of less than 160 μm and an average smallest clearance between the injector needle and injector barrel/casing of less than 10 μm. Such designs have made injectors more sensitive to fuel particulate contamination. Accordingly, injector performance concerns run across all segments of diesel engine vehicles including, but not limited to, light-duty diesel passenger vehicles, on-road fleets, mining equipment, farming equipment, railroad, and inland marine engines.
There are two distinct types of deposits that have been identified on fuel injectors. One type of deposit is a hard carbonaceous deposit that is seen on the injector tips and on the outside of the fuel injectors. Such carbonaceous deposit is based on fuel degradation. The other type of deposit is a waxy, white to yellow deposit that appears as a thin film on the internal surfaces of high-pressure common rail (HPCR) injector needles and command plungers, primarily in the lowest clearance areas of the injector internals or on the pilot valve of the injectors.
If left untreated, the internal deposits may lead to significant power loss, reduced fuel economy, and, in extreme cases, increased downtime and higher maintenance costs due to premature replacement of “stuck injectors.” The internal deposits are believed to be a result of certain common corrosion inhibitors, biofuel components and acidic friction modifiers, or other carboxylic components used in the fuel interacting with trace amounts of alkali metal salts that form salts that are relatively insoluble in ultra low sulfur diesel (ULSD) fuels compared to the better solubility of such salts in the higher sulfur fuels. The internal deposits may be composed mainly of sodium salts of alkenyl succinic acids. Sodium can enter the diesel fuel from a number of sources including refinery salt drivers, storage tank water bottoms and seawater used as ship ballast. When such salts are present in fuel that is used in a High Pressure Common Rail (HPCR) engines, the salts may tend to deposit in the very tight tolerance areas of the injectors. Such deposits may lead to stuck fuel injectors or poor fuel injection, which in turn may lead to lost power, lost fuel economy, rough running engines, and eventually excessive vehicle downtime and maintenance expense. Many conventional detergents such as succinimide detergents, Mannich detergents and quaternary ammonium salt detergents are not particularly effective at conventional treat rates for removing alkali metal salt deposits from internal components of fuel injectors. Furthermore, the use of such detergents at excessively high treat rates may be detrimental to engine components. Accordingly, there is a continuing need for detergents that are effective for removing internal deposits without detrimentally affecting other engine components.
In accordance with the disclosure, exemplary embodiments provide a method for cleaning up internal components of a fuel injector and for improving injector performance for a diesel engine. The method includes operating the diesel engine on a fuel composition containing (1) a major amount of diesel fuel having a sulfur content of 50 ppm by weight or less and from about 0.1 to 2 ppm by weight of alkali metal as a salt, and (2) from about 45 to about 550 ppm by weight based on a total weight of fuel composition of a fuel additive compound of the formula
wherein R is an alkyl or alkenyl group containing from 20 to 170 carbon atoms. The additive has a total acid number (TAN) ranging from about 50 to about 290 mg KOH/g. The fuel injectors of the fuel injected diesel engine have an average injector hole diameter of less than 160 μm and an average smallest clearance between injector needle and injector barrel/casing of less than about 10 μm. For example, injector clearance of a DW-10C engine is in the range of from about 2.5 to about 3 μm.
Another embodiment of the disclosure provides a method of unsticking fuel injectors of a fuel injected diesel engine and recovering lost engine power due to the presence of internal injector deposits. The method includes operating the diesel engine on a fuel composition that includes (1) a major amount of diesel fuel having a sulfur content of 50 ppm by weight or less and from about 0.1 to 2 ppm by weight of alkali metal as a salt, and (2) from about 45 to about 550 ppm by weight based on a total weight of fuel composition of a fuel additive consisting essentially of a compound of the formula
wherein R is an alkyl or alkenyl group containing from 20 to 170 carbon atoms. The additive has a total acid number (TAN) ranging from about 50 to about 290 mg KOH/g. The fuel injectors of the fuel injected diesel engine have an average injector hole diameter of less than 160 μm and an average smallest clearance between injector needle and injector barrel/casing of less than about 10 μm, wherein the fuel injectors are not stuck after clean up, and wherein at least 20% of lost power is recovered in 8 hours according to a DW10 test using a sodium salt as a dopant.
A further embodiment of the disclosure provides a method for reducing an amount of alkali metal salt deposits on internal components of a fuel injector for a fuel injected diesel engine. The method includes operating the diesel engine on a fuel composition comprising (1) a major amount of fuel containing from about 0.1 to 2 ppm by weight of alkali metal as a salt, and (2) from about 45 to about 550 ppm by weight based on a total weight of fuel composition of a fuel additive consisting essentially of a compound of the formula
wherein R is an alkyl or alkenyl group containing from 20 to 170 carbon atoms. The additive has a total acid number (TAN) ranging from about 50 to about 290 mg KOH/g. The fuel injectors of the fuel injected diesel engine have an average injector hole diameter of less than 160 μm and an average smallest clearance between injector needle and injector barrel/casing of less than about 10 μm.
An advantage of the fuel additive described herein is that the additive may not only reduce the amount of internal deposits forming on direct and/or indirect diesel fuel injectors, but the additive may also be effective to clean up dirty fuel injectors and restore lost engine power. The unexpected benefits of the fuel additive described herein is quite surprising since much higher treat rates are generally required for conventional detergents to be effective for cleaning up dirty fuel injectors and/or restoring engine power.
Additional embodiments and advantages of the disclosure may be set forth in part in the detailed description which follows, and/or may be learned by practice of the disclosure. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure, as claimed.